1. Field of the Invention
This invention relates to a sphygmogram measure method and device, which allows a user to determine pulse pressure at two adjacent points.
2. Description of Prior Art
Conventional methods of sphygmogram rely on measuring the pressure of the pulse and the variation of the waveform, or changing the pressure into spectrums for analysis, to evaluate the health status of a person. In addition, Doppler ultrasound to measure blood flow, and measuring the velocity of red blood cell using infrared were also used. However, these methods would only obtain single data at one time period, instead of multiple signals simultaneously. Single data of pulse pressure, blood flow, or flow rate was insufficient for expressing all aspects of cardiovascular status, because the same pulse pressure may yield different blood flow due to different diameter or compliance of vessel. Furthermore, the health status and hemokinetics are closely related that the changes cannot be accurately understood by single data of pulse pressure, flow rate or flow velocity.
Suppose that the bloodstream is a laminar flow and the vessel is a linear resilient tube, a formula of blood flow rate is as follow:   Q  =            π              20        ⁢        α        ⁢                                   ⁢        L        ⁢                                   ⁢        μ              ⁡          [                                    (                                          a                0                            +                                                α                  ⁢                                                                           ⁢                                                            P                      0                                        ⁡                                          (                      t                      )                                                                      2                                      )                    5                -                              (                                          α                0                            +                                                α                  ⁢                                                                           ⁢                                                            P                      L                                        ⁡                                          (                      t                      )                                                                      2                                      )                    5                    ]      Wherein:
Q is the blood flow rate;   α  =            Δ      ⁢                           ⁢      a        p  is the vessel compliance Δa is the variation of the vessel diameter and p is the pulse pressure value;
L is the distance between two measure points;
μ is the blood viscosity coefficient;
a0 is the unstressed vessel diameter; and
P0(t) and PL(t) are the pulse pressure values of two measure points.
Therefore, the values of the vessel compliance α, the blood viscosity coefficient μ, the vessel diameter a0, the pulse pressure values of the two measure points P0(t) and PL(t), and the distance between the two measure points L are essential to calculate the blood flow rate from the above formula. Conventional measure methods and devices are unable to provide simultaneously all the above data in a single process by the same device.
Theoretically, to obtain the blood flow rate in accordance with above formula, the shorter the distance between two measure points is, the more accurate the estimate of blood flow rate can be. But it will be more difficult to measure pulse pressures of two measure points when the distance is closed. According to traditional Chinese medicine, the two measure points must be within one fingertip, that is, the distance between the two measure points will be appropriate between 2 to 3 mm. Refer to FIG. 1, the pulse wave velocity (PWV) in human radial artery at wrist is about 3.5 to 4.5 m/sec, which the pulse takes approximately 0.5 millisecond to pass through these two points; and most of current-in-used sphygmorgrah devices sample the pulse pressure by frequencies from 200 to 400 Hz, i.e. a period from 20 to 50 millisecond, which obviously indicates that these devices are not able to distinguish the difference of pulse pressures at these closed points.
Besides, the difference of pulse pressure between two adjacent points is rather small, it makes difficult to convert pulse pressures from analog signal into digital signal with satisfied resolutions.
Another important factor affecting the outcome of calculation for blood flow rate is vessel compliance α. A research on carotid artery shows that practical vessel compliance is non-linear which varies during arterial systole and diastole. It means that the above formula should be modified, because the vessel compliance α is no longer a constant value.
Based upon the definition of the vessel compliance, the ratio of the variation of vessel's diameter to the pulse pressure, or the slope of a variation of vessel's diameter and pulse pressure curve at measure point, intuitionally, it seems simply install a pressure sensor and a displacement sensor at measure point to acquire the pulse pressure signal and the variation of vessel's diameter signal and then to calculate the nonlinear vessel compliance in a digital processing unit. But in reality, it is not applicable for noninvasive solution: at measure point, a pressure sensor should be holding stationary at certain depth against the vessel to have pressure signals and a displacement sensor should be placed to sense the variations of the vessel's diameter. A stationary pressure sensor and a movable displacement sensor cannot be connected together to have both pressure and variations of vessel's diameter at same measure point which results in failure of computing nonlinear vessel compliance.
As mentioned above, the conventional methods and devices can acquire neither the values of two pulse pressures P0(t) and PL(t), nor the vessel compliance α.
Accordingly, there is a need for an improved sphygmogram measure method and device, which provide solutions to the disadvantages of current counterparts.